They could do Mr. Freeze as more realistic. Firstly, they would need to treat the characterization the way that Batman: The Animated Series did; a more serious and sympathetic tone. His more unrealistic elements could be trimmed to a simple liquid nitrogen spray gun and a suit to carry the liquid and protect from backwash.

As for the wife, she would really just be dead and he couldn't accept it.

And the freezing aspect could be used for motivation

"I want those that turned their back's on my wife and I to feel their coldness...."